(a) Field of the Invention
The present invention relates to a display device which comprises a display panel including a display substrate, an IC mounting substrate which is arranged along the side edge of the display substrate and provided with a display driving IC mounted thereon by face-down bonding and a substrate connecting part for connecting these substrates.
(b) Description of Related Art
Various techniques have been developed for the purpose of downsizing, weight reduction and sliming down of liquid crystal displays, e.g., a face-down bonding technique for mounting liquid crystal driving ICs on a glass substrate of a liquid crystal display panel. There have also been developed techniques for solving a wide variety of problems that occur in connection with these techniques related to the liquid crystal displays.
According to Japanese Unexamined Patent Publication No. 2003-280548, a substrate of a display device is thinned while only a single edge thereof is kept thick. Specifically, a glass substrate is thinned down to 0.3 mm in thickness by mechanical polishing while a single edge thereof is kept thick. Then, the substrate is further thinned down to 0.05 mm in thickness by chemical polishing and a substrate reinforcement layer such as a polarizer or the like is arranged at the thinned part. According to this technique, a flexible display device is obtained. External connection terminals are arranged at the thick edge, thereby preventing poor connection from occurring.
Japanese Unexamined Patent Publication No. H9-80406 discloses a liquid crystal display. In the liquid crystal display, the right edge of a lower film substrate protrudes from the right edge of an upper film substrate to form a protrusion and a plurality of connection terminals are arranged on the top surface of the protrusion. Further, cutout portions are formed at both sides of the protrusion so that they are opposed to each other via a bunch of the connection terminals. With this configuration, if a downward bending stress is applied to the protrusion, the protrusion is curved to form an arc by the width of the cutout portions, but not bent or cracked like a conventional liquid crystal display. Accordingly, the connection terminals formed on the protrusion are also curved to form an arc by the width of the cutout portions, thereby preventing poor connection such as a break in wiring traces.
Japanese Unexamined Patent Publication No. H8-186336 discloses a drive circuit module comprising a substrate made of an inflexible hard material, a circuit pattern which is formed on the substrate and provided with a plurality of input terminals and output terminals supported on a flexible insulating film and a mounting part for mounting driving LSIs on the circuit pattern. On the surface opposite to the surface formed with the circuit pattern, the substrate is provided with at least one cut such that the substrate can be bent at the cut, whereby the surface formed with the output terminals and the surface formed with the mounting part are faced to different directions. The publication describes that this configuration allows reduction in outer size of the liquid crystal display and avoids misalignment of the output terminals of the drive circuit module to be connected with wiring terminals of a liquid crystal display panel.
Japanese Unexamined Patent Publication No. H7-36053 discloses a technique, in which a liquid crystal display panel and a circuit board are connected via a TAB (tape automated bonding) which includes a number of foil-shaped leads supported on a flexible insulating film and slits formed in the center thereof, the circuit board is shifted rearward from the liquid crystal display panel by bending the TAB at the slits, and then a protective film is formed to cover the slits. Since the TAB is bent at the slits, it is bent at a small radius of curvature. Further, since the foil-shaped leads exposed at the slits are covered with the protective film, the leads are prevented from breaks and short circuits caused by external force or adhesion of conductive foreign objects. Moreover, since the protective film fixes the bending status of the TAB, restitution of the flexible film of the TAB is surely controlled.
Japanese Unexamined Patent Publication No. H3-168618 describes that linear spacers are arranged in a stripe pattern on a substrate made of plastic or the like while the lengthwise direction of the spacers are aligned with the direction of maximum curvature of the substrate. Thus, a curved liquid crystal panel is obtained in which a liquid crystal layer keeps its thickness uniform even if the panel is greatly curved.
Japanese Unexamined Patent Publication No. H10-339866 discloses a rollable liquid crystal display using a plastic substrate in which a liquid crystal display driving section is gathered at one end of a first substrate. According to this configuration, the liquid crystal display is reduced in size, thereby obtaining portability.
Japanese Unexamined Patent Publication No. 2003-66474 discloses that conversion wiring traces are formed on a planarized layer and every electrode terminal is localized at one end of a liquid crystal display panel, thereby making the liquid crystal display panel suitable for one-side mounting. With this configuration, display devices for cellular phones and the like are reduced in size.
Japanese Unexamined Patent Publication No. 2000-312070 discloses that ones of extraction electrode terminals on a liquid crystal display panel and output electrode terminals on a flexible substrate are arranged at a fixed pitch. Depending on the thermal expansion coefficient of the flexible substrate, the other terminals are arranged at such a pitch that becomes large from the middle of the length of the terminal region towards the peripheral ends thereof. According to this configuration, when the flexible substrate is thermocompression-bonded to the terminals of the liquid crystal display panel via an anisotropic conductive film, poor connection caused by elongation of the flexible substrate is drastically reduced.
When a liquid crystal display panel is used for an electronic book or a cylindrical display, or when it is used on a flat surface and external force is applied thereto, bending deformation may be applied to the liquid crystal display panel.
If a liquid crystal driving IC is mounted on a plastic substrate by face-down bonding and bending deformation is applied to the liquid crystal display panel, the liquid crystal driving IC may come off the plastic substrate together with a coating layer formed on the plastic substrate. This is because of low adhesion strength between the coating layer and the plastic substrate.
The liquid crystal driving IC itself is not bendable. Therefore, even if a plastic substrate is used, bending deformation which can be applied to the liquid crystal display panel is limited by the liquid crystal driving IC.